Electric discharge tube



Aug. 17, 1954 R, LOOSJES 2,686,886

ELECTRIC DISCHARGE TUBE Filed Oct. 5, 1950 INVENTOR.

AGENT Patented Aug. 17, 1954 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE TUBE Robert Loosjes, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application October 5, 1950, Serial No. 188,519

4 Claims. I

This invention relates to electric discharge tubes comprising a. cathode activated by one or more alkaline earth metal oxides.

It is known that, in electric discharge tubes, the grids and possibly also the anode of a tube may tend to emit electrons thermally. This is because the grids are heated by the cathode and, probably also from the anode, while the anode itseL is heated by the anode current and because alkaline earth metal and/or oxide evaporated from the cathode produce an electron-emitting layer on the grids and the anode. To prevent the primary emission thus produced, it is known to coat the grids with a thin layer of gold. This has the disadvantage that gOld is comparatively volatile so that it readily evaporates and in consequence the grids may tend to emit thermally and the cathode may be poisoned. Moreover the use of gold is comparatively expensive.

Ihe object of the present invention is to provide an alternative and improved means for preventing such primary emission in tubes having a cathode activated by alkaline earth metal oxides.

According to the invention, a tube comprises a cathode activated by alkaline earth metal oxides, and has at least one grid and/or the anode consisting at the surface of a thin layer of thorium in the non-oxidised condition.

It has been found that in tubes according to the invention, the grids have approximately the same low thermal grid-emission as in tubes in which the grids are coated with gold.

In order to reduce the electron-emission of anodes, it is known to coat them with thorium in an oxidised condition. However, the electronemission is not prevented to a sufiicient degree by this means upon vaporization of barium from the cathode.

In tubes having a tungsten-thorium cathode,

it is furtherfore known to coat a water-cooled the need for the invention is not present due to the absence of alkaline earth metal oxides.

In the drawing I designates an evacuated glass tube, 2 is an oxide coated spiralised cathode, 3 is the grid and 4 the anode. On the grid bars and the anode surface is sintered a layer of thorium powder 5, respectively 6, if preferred in an atmosphere of hydrogen. The thorium may also be applied by evaporating it to the grid and anode in a special vessel.

What I claim is: l

1. An electric discharge tube comprising a cathode activated With alkaline earth metal oxides, and an electrode having a thin surface layer of non-oxidized thorium to suppress thermal electron emission therefrom.

2. An electric discharge tube comprising a cathode activated with alkaline earth metal oxides, a grid, and an anode having a thin surface layer of non-oxidized thorium to suppress thermal electron emission from the anode.

3. An electron discharge tube comprising a cathode activated with alkaline earth metal oxides, a grid having a thin surface layer of nonoxidized thorium to suppress thermal electron emission therefrom, and an anode.

4. An electron discharge tube comprising a cathode activated with alkaline earth metal oxides, a grid having a thin surface coating of nonoxidized thorium, and an anode having a thin surface coating of non-oxidized thorium, said thorium coatings suppressing thermal electron emission from said grid and anode electrodes.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,670,487 Thomas May 22, 1928 1,733,813 Marden Oct. 29, 1929 1,760,454 Ulrey May 27, 1930 1,787,694 Marden Jan. 6, 1931 1,858,676 McCullough May 17, 1932 1,893,304 Rentschler et a1 Jan. 3, 1933 2,091,554 Mendenhall Aug. 31, 1937 

1. AN ELECTRIC DESCHARGE, TUBE COMPRISING A CATHODE ACTIVATED WITH ALKALINE EARTH METAL OXIDES, AND AN ELECTRODE HAVING A THIN SURFACE LAYER OF NON-OXIDIZED THORIUM TO SUPPRESS THERMAL ELECTRON EMISSION THEREFROM. 